Telling overweight people to eat healthily does not work because their brains override rational advice when presented with food, the University of Cambridge has found.
Although the government and NHS has attempted to educate people with healthy eating campaigns, the researchers say that removing temptation is probably the best solution.
The study found that both lean and overweight people were aware of which foods are nutritious and were inclined to choose healthier options in a computer-based task.
“The presence of unhealthy food options is likely to override people’s decisions.”
Dr Nenad Medic from the Department of Psychiatry
But when presented with a buffet of real food, the overweight people ate far more unhealthy foods than the thinner participants.
“There’s a clear difference between hypothetical food choices that overweight people make and the food they actually eat,” says Dr Nenad Medic from the Department of Psychiatry.
“Even though they know that some foods are less healthy than others and say they wouldn’t necessarily choose them, when they are faced with the foods, it’s a different matter.
“This is an important insight for public health campaigns as it suggests that just trying to educate people about the healthiness of food choices is not enough.
“The presence of unhealthy food options is likely to override people’s decisions. In this respect, food choice does not appear to be a rational decision - it can become divorced from what the person knows and values.”
The inability to pick healthy foods appears to stem from differences in the brain. In a second study, the researchers looked at the brain structure of over 200 healthy individuals using an MRI scanner and found an association between body mass index (BMI) and brain structure.
In particular, an area of the brain linked to rational thought and decision making – the ventromedial prefrontal cortex - was found to have less grey matter in people with high BMI.
“Perhaps this offers us some clues about the first observation – that rational, hypothetical valuation decisions don’t fully translate into healthy choices in the overweight people when they are offered real food choices,” says Professor Paul Fletcher from the Department of Psychiatry.
“While the region is clearly responding in a way that is not distinct from leaner people, perhaps the structural differences suggest a reduced ability to translate what one knows into what one chooses.
“Although we can only speculate at this stage, and we really don’t know, for example, whether this brain change is a cause or a consequence of increased weight, this could help explain why this same group of people found it harder to stick to their original, healthier food choices when presented with a buffet selection.”
A recent study, published in The Lancet, found that Britain will be the fattest country in Europe by 2025, with nearly four in 10 people clinically obese.
Professor Theresa Marteau, Director of the Behaviour and Health Research Unit at the University of Cambridge, a co-author of the study, adds: "These findings attest to the power of environments in overwhelming many people’s desires and intentions to eat more healthily.
“The findings also reinforce the growing evidence that effective obesity policies are those that target food environments rather than education alone.”
The two pieces of research were published in the online journal eNeuro and the International Journal of Obesity.